Thanks for the link(s) , maybe the ground should have less contrast to make the sprites stand out more?
If anything the sprites should have a less fine detail then the background.
The problem is when you put little dots of different colors next to each other and zoom out it looks grainy, which looks bad and flattens the image. Especially when you outline the whole thing in black.
To get inspiration I have looked a lot on the sprites from Master of Magic, they are really small and have great diversity
I thought of MOM when I saw these, but MOM sprites were also grainy.
The sprites are good, but your shoving too much detail into them for their size.